In recent years, global warming due to an increase in the amount of emission of carbon dioxide is a problem. Even in the steel industry, reducing the amount of emitted CO2 is an important issue. Therefore, in recent operations of blast furnaces, low reducing agent rate (low RAR) operations are greatly encouraged. (The reducing agent rate is the total amount of reducing agent blown in from a tuyere and coke fed from the top of a furnace, per 1 ton of pig iron manufactured). In a blast furnace, coke and pulverized coal injected from a tuyere are primarily used as reducing agents. To achieve a low reducing agent rate and, thus, suppress the amount of emission of carbon dioxide, it is effective to replace, for example, coke with a reducing agent having a high hydrogen content such as waste plastic, LNG, and heavy oil. Japanese Unexamined Patent Application Publication No. 2006-291251 below discusses that, when two or more lances that inject reducing agents from a tuyere are used and a flammable reducing agent such as LNG, and a solid reducing agent, such as pulverized coal, are injected from different lances, the lances are disposed so that an extension line of a lance that injects the flammable reducing agent and an extension line of a lance that injects the solid reducing agent do not cross each other.
Although, compared to a conventional method of injecting only pulverized coal from a tuyere, the method of operating a blast furnace in Japanese Unexamined Patent Application Publication No. 2006-291251 has the effect of increasing combustion temperature and reducing a unit consumption of reducing agent, it can be further improved.
It could therefore be helpful to provide a method of operating a blast furnace that makes it possible to further increase combustion temperature and reduce unit consumption of reducing agents.